Timber framing has its own vocabulary, and the terms do more than label parts: they describe how a building stands up. A frame is assembled from vertical posts, horizontal beams, trusses, and bents, and every member has a defined job in carrying structural weight. Knowing the vocabulary lets you read a floor plan, talk to an engineer, and judge whether a proposed design makes sense. The fundamentals of structural timber engineering start with these members, whether they are sawn lumber, glulam, or cross-laminated timber.
A timber frame differs from a log home and from stick framing. Log homes stack whole logs to form the walls themselves, while timber frames use a skeleton of large members with the spaces between filled by other materials. The frame carries the load and the infill does not, which is why the structural members get the careful engineering.
Vertical Posts: The Legs of the Frame
Posts are the vertical members that act as the legs of the frame, carrying roof and floor loads down to the foundation. Their names describe position and duty: principal posts stand at the corners, while king, queen, and crown posts support specific beams and trusses. Each has a specific role in holding up the members around it.
A Samson post, for example, supports the intersection of four horizontal upper-story beams, a joint where loads arrive from four directions at once. Post selection follows the same logic used in advanced construction materials, where fiber-reinforced polymers, mass timber, and smart materials each earn a place by matching the job.
Post Types and Their Jobs
- Principal posts: corner members that anchor the frame.
- King posts: center posts in trusses that carry the ridge.
- Queen posts: paired posts that widen a truss span.
- Crown posts: short posts rising from a tie beam to a collar.
- Samson posts: support the intersection of four beams.
- Gunstock posts: whole trees turned upside down to use the trunk’s natural flare.
Why the Gunstock Post Uses the Tree’s Flare
A gunstock post, also called a joweled post, is fashioned from a whole tree turned upside down so the wide base of the trunk sits at the top, where the post carries the largest load. The flare provides extra bearing area at the joint without wasting material, and the taper gives the frame its distinctive silhouette.
Horizontal Beams: Sills, Girts, Joists, Purlins, and Ridgepole
Beams run horizontally and tie the frame together at every level. Five members do most of the work, and their names come from position rather than size. Timber sills form the perimeter of floor sections and the surface posts stand on; girts span between posts at intermediate heights, and the word gives us the modern term girder.
Joists support floors, purlins run between exterior posts or tie roof sections together, and the ridgepole sits at the horizontal apex of the roof system. Grading and code rules for these members are spelled out in standards such as the IS codes used for timber and timber stores, which set moisture limits and strength classes for selecting a beam.
Beam Roles in a Frame
| Member | Location | Job |
|---|---|---|
| Sill | Floor perimeter | Supports posts, ties floor |
| Girt | Between posts | Lateral tie, intermediate support |
| Joist | Floor spans | Carries floor loads |
| Purlin | Roof plane | Supports rafters between trusses |
| Ridgepole | Roof apex | Horizontal ridge support |
Sills take the worst moisture exposure of any frame member because they sit closest to grade, so pressure-treated or naturally durable species are common there. Waterproofing between sill and foundation is a standard detail on every timber frame.
Moisture and Shrinkage
Green timbers shrink as they dry, and the movement shows up at the joints. Kiln-dried stock at 15 to 19 percent moisture content moves less after installation, which is why experienced crews let framing timber acclimate on site before cutting joinery.
Sizing a Beam
Beam size depends on span, spacing, and the load above. Doubling the span roughly quadruples the bending stress, so a girt that works at 8 feet may need to grow two nominal sizes at 16 feet. Engineers read these values from published design tables rather than from experience alone.
Trusses: From Simple Triangles to Hammerbeams
A truss is a triangulated frame that spans an opening without intermediate supports. The triangle is the simplest form, but its use is limited to smaller buildings; adding members allows wider spans, and the truss choice shapes the entire interior.
Adding a king post in the center allows a wider span than a plain triangle. Queen-post trusses, in contrast, look like a rectangle within a triangle and reach further still. The hammerbeam truss spans large interior spaces and lets ceilings soar, which is why great rooms and cathedral spaces rely on it. Curved members and curved timber techniques extend what a truss can do, from arched rafters to bowed hammerbeams.
Choosing a Truss by Span
Simple triangular trusses carry spans up to about 20 feet. King-post designs reach 25 to 30 feet, queen-post trusses stretch to 35 feet, and hammerbeam assemblies span 40 feet or more when the joinery is engineered for it. Beyond those ranges, steel flitch plates or glulam members usually take over.
Truss Geometry Matters
Every truss member is either in compression or in tension, and each joint has to carry those forces. That is why truss joinery gets more complex as spans grow and why the truss system is usually the first item an engineer sizes.
Bents: How the Frame Goes Together
When trusses are combined with vertical posts and horizontal beams, the assembly is called a bent. Bents form the basic cross-section of a timber frame and give it the strength to carry structural weight. Raise a series of bents, connect them with purlins and girts, and the frame is complete.
Bents also define the bays that frame the rooms. The spacing between bents, usually 10 to 14 feet in residential work, sets the length of the purlins and the rhythm of the interior, so it is one of the first dimensions an owner reviews.
The comparison to modern systems is direct: cross-laminated timber in tall buildings carries the same gravity and lateral loads through panels that a classic frame carries through bents. The material properties that make mass timber viable at height are the same ones that make a post-and-beam frame durable at house scale.
From Bent to Complete Frame
Assembly follows a fixed order.
- Lay out and assemble each bent flat on the ground.
- Raise the first bent and brace it plumb.
- Raise the remaining bents in sequence.
- Connect the bents with purlins, girts, and ridgepole.
- Set the trusses and lock the frame square.
Joinery Holds It Together
Mortise-and-tenon joints pinned with hardwood pegs are the traditional connection, and modern frames use the same joinery with engineered metal fasteners where loads demand it. The joint, not the timber, usually sets the frame’s capacity.
Timber Grades, Codes, and Modern Engineered Wood
Not every piece of wood can carry a frame. Species, grade, and moisture content determine allowable stresses, and building codes require graded material with a visible grade mark. Douglas fir, oak, and white pine dominate residential timber framing, each with different strength and shrinkage behavior.
Engineered products have changed what a frame can do. LVL and CLT mass timber systems bring factory-controlled strength to mixed-use buildings, and glulam beams bend curves that solid timbers cannot manage. The terminology stays the same, but the members now come from a mill rather than a sawlog.
Grade Marks and Species
Look for the grade stamp on every structural member: it names the grading agency, the species, and the allowable stress. Unmarked stock belongs in decorative work, not in a load path.
Code Paths for Timber
Most jurisdictions work from the International Building Code, which recognizes solid-sawn timber and engineered wood through published design values. A licensed engineer selects members from those tables, which is why the structural review is not optional on a timber frame.
Learning to Read a Timber Frame Drawing
Once the vocabulary is in place, a frame drawing becomes readable: posts show as heavy verticals, beams as horizontals, trusses as triangulated shapes, and bents as the repeated cross-sections. The drawing schedule lists every member, its species, its grade, and its size.
Modern practice builds on the same language with new tools. Cross-laminated timber structural innovations push the old post-and-beam vocabulary into panel systems, but the questions stay the same: what carries the load, and how does it reach the ground?
Reading Order for a Frame Plan
- Find the bent locations on the floor plan.
- Trace the load path from ridgepole to posts to sill.
- Check member sizes against the schedule.
- Confirm truss spans against room widths.
- Ask the engineer about anything that does not line up.
Talk to the Builder in Their Language
Using the correct terms changes how fast a builder or engineer answers your questions. Ask about the purlins before the roof sheathing and the bents before the walls, and the conversation moves from confusion to coordination.